bridge structure

The bridge is 244 m long with two 65 m towers built on pillars. The 61 m central span between the towers is divided into two equal scales or leaves, which can be raised up to an angle of 86 degrees to allow river traffic to pass. The scales, which weigh more than a thousand tons each, have counterweights to minimize the force required and allow them to be lifted in just five minutes. The two side spans are suspension bridges, each 82 m long, whose cables are anchored both in the pillars and through bars on the bridge's upper walkways. The pedestrian walkways are 44 m above the river at high tide.[8]​.

The main deck of the bridge carries two lanes of road traffic between two pedestrian walkways that cross the two suspension spans and the bascule section of the bridge. The causeway passes under the two towers, while pedestrian walkways pass around the outside of the towers. One of the bridge's chimneys, often mistaken for street lamps, is connected to an old chimney in a long-disused guard room at the Tower of London.[25]

Hydraulic system

The original lifting mechanism was powered by pressurized water stored in several hydraulic accumulators. The system was designed and installed by Hamilton Owen Rendel while working for Sir W. G. Armstrong Mitchell & Company of Newcastle upon Tyne. Water, at a pressure of 5.2 MPa, was pumped to the accumulators by two 360 HP (268 kW) double-tandem compound stationary steam engines, equipped with Meyer expansion slide valves. Each accumulator incorporates a 51 cm ram pump in which a very heavy weight is located to maintain the desired pressure.

The entire hydraulic system, together with the gas lighting system, was installed by William Sugg & Co Ltd., the well-known Westminster gas engineers. Gas lighting was initially with open flame burners inside the lanterns, but was soon converted to the incandescent system.[28]​.

In 1974, the original mechanism was replaced by a new electro-hydraulic system, designed by BHA Cromwell House.[13] The only components of the original system still in use are the final pinions, which engage with the frames installed on the scales. These are driven by modern hydraulic motors and a gear, which uses oil instead of water as the hydraulic fluid.[14] Some of the original hydraulic machinery has been preserved, although it is no longer in use. It is open to the public and forms the basis of the bridge museum, which is housed in the old engine rooms on the south side of the bridge. The museum includes the steam engines, two of the accumulators and one of the hydraulic motors that moved the scales, along with other related objects.

Signaling and control

To control the passage of river traffic under the bridge, several different rules and signals have been used. During the day, traffic was controlled by red traffic lights, placed in small control booths at each end of the bridge's two piers. At night, colored lights were used, in each direction, on both towers: two red lights to indicate that the bridge was closed, and two green to indicate that it was open. In fog, a gong was also played.[8]​.

Ships passing through the bridge also had to show signs: during the day, they had to place a black ball of at least 60 cm in diameter high in sight; at night, two red lights in the same position. If it was foggy they had to repeatedly blow the ship's steam whistle. If a black ball was hung from the center of each gangway (or a red light at night), this indicated that the bridge could not be opened. These signals were repeated about 900 m downstream, at Cherry Garden Pier), where ships needing to pass the bridge had to hoist their signals or lights and sound their horn, as appropriate, to alert the bridgemaster.[8] Some of the Control mechanisms of the signaling equipment have been preserved and can be seen in operation in the bridge museum.

Road

Tower Bridge remains a busy crossing of the Thames: it is crossed by over forty thousand people each day including motorists, cyclists and pedestrians.[16] The bridge is on the London Inner Ring Road), and is on the eastern edge of London's congestion charging zone (the bridge is not included in the zone).

To maintain the integrity of the structure, the City of London Corporation has imposed a speed limit of 20 miles per hour (32 km/h), and a weight limit of 18 tonnes for vehicles using the bridge. A camera system measures the speed of traffic crossing the bridge using a license plate recognition system to issue tickets to speeding drivers.[30] A second system monitors other vehicle parameters, and uses detectors. induction loop and piezoelectric sensors to measure weight, chassis height above ground level and the number of axles of each vehicle.[30]​.

River

The scales are raised about a thousand times a year.[31] River traffic has been greatly reduced, but it still has priority over road traffic. Currently, 24 hours' notice is required for the bridge to open, and opening times are published in advance on its website.[32]​.

The Tower Bridge Exhibition is an exhibition located in the twin towers of the bridge, the walkways between the towers and the Victorian engine rooms. Use films, photographs and interactive displays to explain why and how Tower Bridge was built. Visitors can access the original steam engines that once powered the bridge scales, located in a building near the south end of the bridge.[15]​.

The exhibition charges an entrance fee. Entrance is from the west side of the bridge deck via the north tower, from where visitors ascend to the fourth floor by elevator before crossing the walkways to the south tower. On the towers and walkways there is an exhibition about the history of the bridge. The walkways also provide views over the city, the Tower of London and the Pool of London, and have a glass-floored section. From the south tower, visitors can visit the engine rooms, home to the original steam engines, which are located in a separate building adjacent to the south approach to the bridge.[33]​.

Although Tower Bridge is undoubtedly an iconic London landmark, professional commentators at the turn of the century were critical of its aesthetics. "It represents the vice of kitsch and pretentiousness, and the falsification of the real facts of the structure," wrote Henry Heathcote Statham"),[34] while Frank Brangwyn stated: "A more absurd structure than Tower Bridge has never been built to cross a strategic river."[35]

On the other hand, Benjamin Crisler, the film critic of the New York Times, wrote in 1938: "The British have three unique and valuable institutions that we in America do not have: Magna Carta, Tower Bridge and Alfred Hitchcock."[36]​.

Architectural historian Dan Cruickshank selected Tower Bridge as one of his four structures for the 2002 BBC television documentary series Britain's Best Buildings.

Tower Bridge is often confused with London Bridge,[38]​ the next bridge upstream of the Thames. A popular urban legend claims that in 1968, Robert P. McCulloch, the buyer of the former London Bridge&action=edit&redlink=1 "London Bridge (Lake Havasu City) (not yet redacted)") that was transported to Lake Havasu City, Arizona, believed he was purchasing Tower Bridge. This was denied by McCulloch himself and has been discredited by Ivan Luckin, the seller of the bridge.[39]​.

A partial replica of the Tower Bridge has been built in the city of Suzhou (China). The replica differs from the original in that it has no lifting mechanism and has four separate towers.[40]​.

On August 10, 1912 Francis McClean") flew between the scales and gangways with his Short Brothers S.33 flying boat.[41]​[42]​.

In December 1952, the bridge opened while a double-decker bus was crossing it from the south bank. At that time, the gatekeeper had to ring a warning bell and close the gates when the bridge was empty, before the watchman ordered the bridge to be raised. The process failed while a relief guard was on duty. The bus was near the edge of the south scale when it began to rise; Driver Albert Gunter made the decision to accelerate in a fraction of a second, crossing a gap of one meter to fall almost two meters towards the north scale, which had not yet begun to rise. There were no serious injuries.[43]​[44]​ The City Corporation rewarded Gunter with ten pounds (equivalent to £306 today) for his act of bravery.[45]​.

On 5 April 1968 a Hawker Hunter FGA.9 fighter aircraft of the Royal Air Force's 1st Squadron "1st Squadron RAF (UK)", piloted by Alan Pollock, flew across Tower Bridge. Disappointed that the RAF was not going to celebrate its fiftieth birthday with an air parade, Pollock decided to do something himself. Without authorization, Pollock flew the Hunter at low altitude along the Thames, past the Palace of Westminster, and continued towards Tower Bridge by passing under the footbridge, later commenting that it was an afterthought when he saw it approaching the bridge. Pollock was placed under arrest upon landing, and expelled from the RAF for health reasons without the possibility of defending himself at a court-martial.[46][47]​.

In the summer of 1973, a Beagle Pup aircraft flew twice under the Tower Bridge pedestrian walkway, piloted by 29-year-old stock secretary Paul Martin. Martin was free on bail following accusations of securities fraud. He subsequently flew over several buildings in the City, before flying north towards the Lake District, where he died when his plane crashed about two hours later.[48]

In May 1997,[49] United States President Bill Clinton's "Presidential Limousine (United States)" motorcade was split in two by the opening of the bridge. The sailing barge Gladys, on its way to a meeting at St Katharine Docks, arrived on time and the bridge opened for her. Returning from a Thames-side lunch at the restaurant Le Pont de la Tour with UK Prime Minister Tony Blair, Clinton was less than punctual and arrived just as the bridge was being raised. The opening of the bridge split the motorcade in two, to the dismay of security staff. A Tower Bridge spokesperson is quoted as saying: "We tried to contact the United States embassy, but they did not answer the phone."[50]​.

On 19 August 1999, Jef Smith, a freeman&action=edit&redlink=1 "Freeman (person) (not yet redacted)") from the City of London, led a flock of two sheep across the bridge. He was exercising an ancient reclaimed permission, granted as a right to freemen, to reflect on the powers of older citizens and the way in which their rights were being eroded.[51]​.

On October 31, 2003 before dawn, David Crick, a Fathers 4 Justice activist, scaled a hundred-foot tower crane near Tower Bridge at the start of a six-day protest dressed as Spider-Man. Fearing for his safety and that of motorists should he fall, police cordoned off the area, closing the bridge and surrounding streets, causing widespread traffic congestion. throughout the City and east London. London's Metropolitan Police was later criticized for maintaining the closure for five days when, in the eyes of some citizens, it was not strictly necessary.[53][54]​.

On May 11, 2009, six people were trapped and injured after an elevator fell three meters into the north tower.[55]​.

• - Mobile bridge.

• - HMS Belfast "HMS Belfast (C35)").

• - London Bridge.

• - Tower of London.

• - Wikimedia Commons hosts a multimedia category on Tower Bridge.

• - Official website.

• - Bridge Lift Times.

• - You describe the construction of Tower Bridge.

bridge structure

The bridge is 244 m long with two 65 m towers built on pillars. The 61 m central span between the towers is divided into two equal scales or leaves, which can be raised up to an angle of 86 degrees to allow river traffic to pass. The scales, which weigh more than a thousand tons each, have counterweights to minimize the force required and allow them to be lifted in just five minutes. The two side spans are suspension bridges, each 82 m long, whose cables are anchored both in the pillars and through bars on the bridge's upper walkways. The pedestrian walkways are 44 m above the river at high tide.[8]​.

The main deck of the bridge carries two lanes of road traffic between two pedestrian walkways that cross the two suspension spans and the bascule section of the bridge. The causeway passes under the two towers, while pedestrian walkways pass around the outside of the towers. One of the bridge's chimneys, often mistaken for street lamps, is connected to an old chimney in a long-disused guard room at the Tower of London.[25]

Hydraulic system

The original lifting mechanism was powered by pressurized water stored in several hydraulic accumulators. The system was designed and installed by Hamilton Owen Rendel while working for Sir W. G. Armstrong Mitchell & Company of Newcastle upon Tyne. Water, at a pressure of 5.2 MPa, was pumped to the accumulators by two 360 HP (268 kW) double-tandem compound stationary steam engines, equipped with Meyer expansion slide valves. Each accumulator incorporates a 51 cm ram pump in which a very heavy weight is located to maintain the desired pressure.

The entire hydraulic system, together with the gas lighting system, was installed by William Sugg & Co Ltd., the well-known Westminster gas engineers. Gas lighting was initially with open flame burners inside the lanterns, but was soon converted to the incandescent system.[28]​.

In 1974, the original mechanism was replaced by a new electro-hydraulic system, designed by BHA Cromwell House.[13] The only components of the original system still in use are the final pinions, which engage with the frames installed on the scales. These are driven by modern hydraulic motors and a gear, which uses oil instead of water as the hydraulic fluid.[14] Some of the original hydraulic machinery has been preserved, although it is no longer in use. It is open to the public and forms the basis of the bridge museum, which is housed in the old engine rooms on the south side of the bridge. The museum includes the steam engines, two of the accumulators and one of the hydraulic motors that moved the scales, along with other related objects.

Signaling and control

To control the passage of river traffic under the bridge, several different rules and signals have been used. During the day, traffic was controlled by red traffic lights, placed in small control booths at each end of the bridge's two piers. At night, colored lights were used, in each direction, on both towers: two red lights to indicate that the bridge was closed, and two green to indicate that it was open. In fog, a gong was also played.[8]​.

Ships passing through the bridge also had to show signs: during the day, they had to place a black ball of at least 60 cm in diameter high in sight; at night, two red lights in the same position. If it was foggy they had to repeatedly blow the ship's steam whistle. If a black ball was hung from the center of each gangway (or a red light at night), this indicated that the bridge could not be opened. These signals were repeated about 900 m downstream, at Cherry Garden Pier), where ships needing to pass the bridge had to hoist their signals or lights and sound their horn, as appropriate, to alert the bridgemaster.[8] Some of the Control mechanisms of the signaling equipment have been preserved and can be seen in operation in the bridge museum.

Road

Tower Bridge remains a busy crossing of the Thames: it is crossed by over forty thousand people each day including motorists, cyclists and pedestrians.[16] The bridge is on the London Inner Ring Road), and is on the eastern edge of London's congestion charging zone (the bridge is not included in the zone).

To maintain the integrity of the structure, the City of London Corporation has imposed a speed limit of 20 miles per hour (32 km/h), and a weight limit of 18 tonnes for vehicles using the bridge. A camera system measures the speed of traffic crossing the bridge using a license plate recognition system to issue tickets to speeding drivers.[30] A second system monitors other vehicle parameters, and uses detectors. induction loop and piezoelectric sensors to measure weight, chassis height above ground level and the number of axles of each vehicle.[30]​.

River

The scales are raised about a thousand times a year.[31] River traffic has been greatly reduced, but it still has priority over road traffic. Currently, 24 hours' notice is required for the bridge to open, and opening times are published in advance on its website.[32]​.

The Tower Bridge Exhibition is an exhibition located in the twin towers of the bridge, the walkways between the towers and the Victorian engine rooms. Use films, photographs and interactive displays to explain why and how Tower Bridge was built. Visitors can access the original steam engines that once powered the bridge scales, located in a building near the south end of the bridge.[15]​.

The exhibition charges an entrance fee. Entrance is from the west side of the bridge deck via the north tower, from where visitors ascend to the fourth floor by elevator before crossing the walkways to the south tower. On the towers and walkways there is an exhibition about the history of the bridge. The walkways also provide views over the city, the Tower of London and the Pool of London, and have a glass-floored section. From the south tower, visitors can visit the engine rooms, home to the original steam engines, which are located in a separate building adjacent to the south approach to the bridge.[33]​.

Although Tower Bridge is undoubtedly an iconic London landmark, professional commentators at the turn of the century were critical of its aesthetics. "It represents the vice of kitsch and pretentiousness, and the falsification of the real facts of the structure," wrote Henry Heathcote Statham"),[34] while Frank Brangwyn stated: "A more absurd structure than Tower Bridge has never been built to cross a strategic river."[35]

On the other hand, Benjamin Crisler, the film critic of the New York Times, wrote in 1938: "The British have three unique and valuable institutions that we in America do not have: Magna Carta, Tower Bridge and Alfred Hitchcock."[36]​.

Architectural historian Dan Cruickshank selected Tower Bridge as one of his four structures for the 2002 BBC television documentary series Britain's Best Buildings.

Tower Bridge is often confused with London Bridge,[38]​ the next bridge upstream of the Thames. A popular urban legend claims that in 1968, Robert P. McCulloch, the buyer of the former London Bridge&action=edit&redlink=1 "London Bridge (Lake Havasu City) (not yet redacted)") that was transported to Lake Havasu City, Arizona, believed he was purchasing Tower Bridge. This was denied by McCulloch himself and has been discredited by Ivan Luckin, the seller of the bridge.[39]​.

A partial replica of the Tower Bridge has been built in the city of Suzhou (China). The replica differs from the original in that it has no lifting mechanism and has four separate towers.[40]​.

On August 10, 1912 Francis McClean") flew between the scales and gangways with his Short Brothers S.33 flying boat.[41]​[42]​.

In December 1952, the bridge opened while a double-decker bus was crossing it from the south bank. At that time, the gatekeeper had to ring a warning bell and close the gates when the bridge was empty, before the watchman ordered the bridge to be raised. The process failed while a relief guard was on duty. The bus was near the edge of the south scale when it began to rise; Driver Albert Gunter made the decision to accelerate in a fraction of a second, crossing a gap of one meter to fall almost two meters towards the north scale, which had not yet begun to rise. There were no serious injuries.[43]​[44]​ The City Corporation rewarded Gunter with ten pounds (equivalent to £306 today) for his act of bravery.[45]​.

On 5 April 1968 a Hawker Hunter FGA.9 fighter aircraft of the Royal Air Force's 1st Squadron "1st Squadron RAF (UK)", piloted by Alan Pollock, flew across Tower Bridge. Disappointed that the RAF was not going to celebrate its fiftieth birthday with an air parade, Pollock decided to do something himself. Without authorization, Pollock flew the Hunter at low altitude along the Thames, past the Palace of Westminster, and continued towards Tower Bridge by passing under the footbridge, later commenting that it was an afterthought when he saw it approaching the bridge. Pollock was placed under arrest upon landing, and expelled from the RAF for health reasons without the possibility of defending himself at a court-martial.[46][47]​.

In the summer of 1973, a Beagle Pup aircraft flew twice under the Tower Bridge pedestrian walkway, piloted by 29-year-old stock secretary Paul Martin. Martin was free on bail following accusations of securities fraud. He subsequently flew over several buildings in the City, before flying north towards the Lake District, where he died when his plane crashed about two hours later.[48]

In May 1997,[49] United States President Bill Clinton's "Presidential Limousine (United States)" motorcade was split in two by the opening of the bridge. The sailing barge Gladys, on its way to a meeting at St Katharine Docks, arrived on time and the bridge opened for her. Returning from a Thames-side lunch at the restaurant Le Pont de la Tour with UK Prime Minister Tony Blair, Clinton was less than punctual and arrived just as the bridge was being raised. The opening of the bridge split the motorcade in two, to the dismay of security staff. A Tower Bridge spokesperson is quoted as saying: "We tried to contact the United States embassy, but they did not answer the phone."[50]​.

On 19 August 1999, Jef Smith, a freeman&action=edit&redlink=1 "Freeman (person) (not yet redacted)") from the City of London, led a flock of two sheep across the bridge. He was exercising an ancient reclaimed permission, granted as a right to freemen, to reflect on the powers of older citizens and the way in which their rights were being eroded.[51]​.

On October 31, 2003 before dawn, David Crick, a Fathers 4 Justice activist, scaled a hundred-foot tower crane near Tower Bridge at the start of a six-day protest dressed as Spider-Man. Fearing for his safety and that of motorists should he fall, police cordoned off the area, closing the bridge and surrounding streets, causing widespread traffic congestion. throughout the City and east London. London's Metropolitan Police was later criticized for maintaining the closure for five days when, in the eyes of some citizens, it was not strictly necessary.[53][54]​.

On May 11, 2009, six people were trapped and injured after an elevator fell three meters into the north tower.[55]​.

• - Mobile bridge.

• - HMS Belfast "HMS Belfast (C35)").

• - London Bridge.

• - Tower of London.

• - Wikimedia Commons hosts a multimedia category on Tower Bridge.

• - Official website.

• - Bridge Lift Times.

• - You describe the construction of Tower Bridge.